In cable television systems, audio, video and data are distributed and collected through a coaxial cable network to and from the subscribers both directions, downstream and upstream. Simultaneously, alternating current (“AC”), typically 50 or 60 Hz power may be fed through the coaxial cables for powering trunk line amplifiers. A multi tap box connected on the main coaxial line of the network allows most of the RF signal to pass through it while, at one of its ports, a small portion of the RF signal is tapped and routed to a subscriber. A multi tap box is typically equipped with one main line input, one main line output and two or more tap ports.
Since the CATV (Cable Television) network is connected to many subscribers over the coaxial network, many taps should be connected to the main line. It is obvious that low loss through the main line of the multi tap box is essential to the network. At the same time, the frequency response should be as flat as possible i.e. as much as possible indifferent to the frequency. Any loss on the main line of the multi tap multiplies by the number of the multi taps on the line. The overall loss should be as small as a fraction of a decibel over the operational frequency range otherwise service degradation will result. As the number of taps used increases the higher the loss which results in non-flat response, a lower data rate inferior service quality.
Historically, multi tap designers struggled for many years to minimize the loss and to improve the flatness of the frequency response. Inside the multi tap box, at the main line input port, RF chocks and capacitors are typically used to separate the broadband RF signal from the AC power signal. The same arrangement is used for recombining the broadband RF signal with the AC power at the main line output port.
FIG. 1 illustrates a block diagram of a general prior art 5 to 1000 MHz legacy multi-tap device. The combined RF signal and AC power is applied from the main line coaxial distribution cable to the multi tap via main line IN connector 1. Inside the multi-tap device the RF power chock 3 bypasses the AC power to the main line distribution cable via main line output connector 2. The RF chock 3 designed very carefully to provide a relatively large impedance to the RF signal and low impedance and loss to the AC power. The AC power is not passed through other components and therefore only RF signal is passed through the other components of the multi tap device. The signal of about 5 to 1000 MHz flows from main line in connector 1 through capacitor 4, directional coupler 5 and capacitor 6 to the main line output connector 2. The high voltage capacitors 4, 6, protect the directional coupler 5 from the passage of AC power and is typically selected to provide relatively low impedance and low loss to the RF signal and high impedance to the AC power. Both the RF chock 3 and capacitors 4, 6, are selected carefully to provide low hum modulation to the RF signal flowing through the coupler 5.
The RF signal applied to main line in connector 1 passes through capacitor 4 to the input of directional coupler 5, which divides the RF signal into two portions. One portion of the RF signal flows to the main line connector 2 through capacitor 6. The second portion 7 is typically a smaller portion of the RF signal which flows to the legacy frequency 5 to 1000 MHz splitting section 8 which distributes the signal to tap ports 9, 10, 11, 12 and over to the subscribers drop lines. The signal splitting section 8 is typically built of (not shown) two way splitting cascaded hierarchical structure producing signals for 2, 4 or 8 etc. subscribers tap ports. Section 8 is shown with four tap ports but may be with 2, 4 or 8 ports, etc.
FIG. 2 illustrates a general prior art wideband multi-tap block diagram. The combined RF signal and AC power applied from the main line coaxial distribution cable to the multi tap via main line IN connector 13. The diplexer 21 divides the signal into two portions low and high frequencies. The low frequency portion passing the 5 to 1000 MHz to the main line out connector 20 through capacitor 15, coupler 16 and capacitor 17 and the low portion of diplexer 22. The AC current flows through RF chock 14 bypassing capacitors 15, 17 and coupler 16. The RF chock 14 is designed very carefully to provide a relatively large impedance to the legacy RF signal 5 to 1000 MHz and low impedance and loss to the AC power. The AC power is not passed through other components and therefore only RF signal is passed through the other components of the multi tap device. This arrangement is similar to legacy multi tap as described in FIG. 1.
The main line signal high frequency 1000 to 3000 MHz ultraband frequency range passing from connector 13 to connector 20 through the high portion of first diplexer 21 coupler 19 and the high portion of the second diplexer 22. The high pass portion of diplexers 21 and 22 includes high voltage capacitors blocking the AC voltage therefore no additional capacitors required.
The second portion 29 is the small coupled portion of the RF signal from the legacy coupler 16 and the second portion 30 of the ultraband RF signal from coupler 19 combined by the third diplexer 23 and fed through the common port 31 to the wideband 5 to 3000 MHz splitting section 24 distributing the signal to tap ports 25, 26, 27, 28 and over to the subscribers drop lines. The signal splitting section 24 is built of (not shown) two way splitting and re splitting hierarchical structure producing signal for 2, 4 or 8 subscribers tap ports. Section 24 is shown with four tap ports but may be with 2, 4 or 8 ports, etc.
The performance of the RF chock and capacitors is the main reason for the loss and flatness. Over the years the performance of multi tap devices have improved due to better RF chocks and better high voltage capacitors. However, by the time better RF chocks and capacitors became commonplace, CATV systems operators required higher frequency bands of operation; that is, frequency band of operation went from 250 MHz in the early days of cable TV to about 1000 MHz today making the multi tap design even more difficult.
The digital age introduced many new services such as internet, Internet protocol television (IPTV), digital video, high definition television broadcasting and video on demand. These services are bandwidth hungry requiring even higher data rates over the coaxial networks, more bandwidth and higher frequency bands of operation as well. To solve the ever increasing hunger for bandwidth cable operators relied on technological improvements such as higher modulation rate standards like QAM1024, video switching and the reuse of the bandwidth of some analog channels. However, these approaches are still not sufficient to satisfy the hunger for wider bandwidths. Also, as a consequence of the operation at higher bandwidth and frequency of operation, the linearity of the line amplifiers and their power consumption increased, requiring higher AC currents to flow through the coaxial network and the multi taps as well. These higher currents rose from 8 to 10, 12 and 15 A causing higher hum modulation as the current via the splitter tap of the multi tap device increased.
One of the proposed solutions for more bandwidth is to use the coaxial cable head end to generate higher frequency signals (i.e., beyond the 1000 MHz,) thus enabling it to carry more downstream and upstream content within a bandwidth that may be as broad as about 2000 MHz beyond the legacy frequency range, i.e. up to 3000 MHz. A main reason for the realization of the proposed solution is the design of new type of multi tap devices which can support a relatively higher frequency range. These multi tap devices were introduced few years ago and the cable industry's demand for these taps has increased over time. Generally, the new taps were built from well known low frequency couplers operating in the range of 5 MHz to 1000 MHz (“legacy”) and another, higher frequency coupler that can operate in the 1250 MHz to 3000 MHz frequency range (“ultra band”). The signals from these couplers are separated and recombined by high frequency diplexers. The AC power passes through RF chock bypassing the lower frequency coupler section. This arrangement requires the use of many parts and complicated tuning procedures resulting in costly device.
The challenge is to create a new multi tap having high frequency performance where the use of chocks and capacitors is eliminated.
For example, a multi tap which eliminates the need for an RF chock and capacitors and a low power coupler. This new power coupler may replace the RF chock, capacitors and the low power coupler. The new power coupler can operate as a single coupler over a bandwidth as high as 5-3000 MHz and may provide low loss, good flatness, good return loss and high port to port isolation. At the same time it may pass through the main line a 15 A AC current with very low hum modulation, as required.